Communication devices are often required to be backwards compatible with devices that operate in accordance with older communication protocols. Specifically, a communication device, designed for a new communication protocol, is said to be backwards compatible if it is capable of sending and receiving data formatted in accordance with older communication protocols. Mandating or designing new communication devices to be backwards compatible allows networks to be gradually and/or smoothly transitioned to new communication protocols.
Ethernet communication devices are one particular type of communication device often required to be backwards compatible. In fact, the Institute of Electrical and Electronics Engineers (IEEE) generally mandates that all Ethernet compliant devices be backwards compatible with older versions of the Ethernet standard. For example, an Ethernet communication device may support several different Ethernet standards, including 10BASE-T (10 Mbit/s), 100BASE-T (100 Mbits/s), 1000BASE-T (1 Gbit/s), 10 Gigabit Ethernet (10 Gbit/s), and 100 Gigabit Ethernet (100 Gbit/s).
Conventional approaches for providing a communication device compliant with both the latest Ethernet standard(s) (e.g., 10 and/or 100 Gigabit Ethernet) and legacy Ethernet standards commonly use a single, current-mode digital-to-analog converter (DAC) for driving transmission lines. While a current-mode DAC provides excellent linearity capable of meeting the stringent requirements of the 10 and 100 Gigabit Ethernet standards, the high linearity comes at a cost of power consumption. Because slower, legacy Ethernet standards do not require such high linearity, power is generally wasted when the communication device is operating in legacy mode.
Therefore, what is needed is an apparatus for increasing power efficiency of backwards compatible communication devices, such as Ethernet communication devices, when operating in legacy mode.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.